Calculating The Number Of Moles Of Chlorine

[StandbySetting]

I just wondered if anyone could help me with this, I'm making my own dechlorinator from Sodium Thiosulfate crystals dissolved in RO water, and I need to know how many moles of chlorine are in my water, so I know how much to dose, the average Chlorine concentration is 0.37 PPM, I will dose double what I theoretically require so the Sodium Thiosulfate is added in an excess to ensure all of the Chlorine is dealt with.

Is my calculation right? There is 0.00037 g/dm-3 so in my tank which has an exact volume of 117.5 decimetres, there would be 0.043475g in 117.5 decimeters.

0.043475/35.453 = 0.00125 moles once rounded, if this value is correct I can then calculate the number of moles of Sodium thiosulfate required to neutralise the chlorine.

Thanks

 

[hensonc4098]

Sounds about right to me Although ppm is parts per million, so does a part count as a gram? I don't really know lol

 

[StandbySetting]

A part would be mg in a L, I converted mg into gramms earlier on, so I think that part is ok.

 

[twodoctors]

Someone's got the units wrong here. Not sure you or me.

1 mole of chlorine (assuming it's Cl2, not Cl-) is 35.4g

Your concentration is 0.37ppm or 0.37mg/ml.

Your tank is 117.5L, or 117500ml.

So the amount of chlorine is 117500ml x 0.37mg/ml = 43475mg = 43.475g

So 43.475g of chlorine is 43.475/35.4 = 1.228 moles.

To make it more interesting for the uninitiated, that's 1.228 x 6.022x10^23 molecules.

Adrian, anaesthetist

A part would be mg in a L, I converted mg into gramms earlier on, so I think that part is ok.

milli is thousand. thousand x thousand = million. So it is milligram per millilitre = parts per million.

 

[StandbySetting]

For the sake of argument 1 litre of water has a mass of 1Kg, so surely 1mg is 1PPM.

 

[twodoctors]

For the sake of argument 1 litre of water has a mass of 1Kg, so surely 1mg is 1PPM.

part of what?

Try googling parts per million.

Adrian

PS Why not just get it off the shelf and not risk the life of your fishes! SeaChem Prime is cheapest by far.

PPS did that myself. Conflicting info. Wiki agrees with me I think. As above is is 1/1000 per 1/1000, or 1 per 1/1000000

 

[StandbySetting]

1mg in one ml can't be 1PPM, it's 1 part per thousand, which is why I used the water as an example, I never normally use dechlorinator anyway as it's not necessary, but I was given some surplus Sodium Thiosulfate crystals so I thought I'd have a go at it.

 

[twodoctors]

Giving me a headache! Maybe I'm wrong on the ppm. I use SI units at work. PPM only in the hobby!

Otherwise I think my calculation is correct. I did say someone's got the unit wrong! Only trying to help.

 

[Bignose]

ppm is a like over like measurement. that is, it is mass over mass (1 mg per kg) or volume over volume (1 mL per kilo-liter or 1000 L). It actually can be widgets over widgets, and is often used in quality metrics: if on average 2.3 per million widgets that are manufactured are bad, the error rate is often reported as 2.3 ppm.

If the density of a liquid is very close to water, then when you dissolve that liquid in water, you can get away with calling ppm close enough to mg/L. But, it isn't exact.

Often dissolving solids in a liquid isn't very accurate either. That said, 0.4 ppm is pretty low, so it may be okay. Probably close enough for a ball park since the exact value is going to fluctuate from day to day anyway, and you're probably going to want to put some extra dechlorinator in as a safety margin.

 

[hensonc4098]

PS Why not just get it off the shelf and not risk the life of your fishes! SeaChem Prime is cheapest by far.

Lol, good point actually

 

[StandbySetting]

I don't require dechlorinator as my water changes are never any larger then 25% of the tanks volume, I got given these crystals for free so I may as well use them.

Thanks for everyone's input, I set up titration apparatus today just to double check that I have everything correct and it worked.

 

[RadaR]

I knew someone that used something similar I believe. Killed all the fish though because as well as taking out the chlorine, it also took out oxygen.
I'm sure you've ensured its safe to use though.

 

[twodoctors]

I know where I went wrong. SI unit for weight is kg. SI for volume is litre. So parts per million is a millionth of a kilogram, hence milligrams per litre.

Adrian

 

[tribalbrit]

WOW!!!! I'm glad I'm a brickllayer and there are 60 bricks per square metre lol.